R ELEMENT X        i. Atomic number - 17          since no. of protons = atomic number of element       ii. Mass number - 35          since mass number = no. of protons + no. of neutrons                                            = 17 + 18 = 35FOR ELEMENT Y (same EXPLANATION as above)         i. Atomic number - 17         ii. Mass number - 37The atomic species are RELATED as they have the same atomic number.Element X and Y represent Chlorine (as Cl atomic number is 17)10B) given, (E.C) Electronic configuration - 2,8,7        therefore, no. of electrons = 2+8+7 = 17         i. Atomic number = 17        since no. of protons = no. of electrons = 17         ii. A valence electron is the number of electrons found in the last shell of an element. The valence electron of the given element is 7Let's check which element has the same number of valence electrons by checking E.C (electronic configuration) of eachEC of Nitrogen (N) - 2,5EC of Fluorine (F) - 2,7EC of PHOSPHORUS (P) - 2,8,4EC of Argon (Ar) - 2,8,8So, only Fluorine (F) has the same number of valence electrons, 7I really HOPE this helped you out! I spent a lot of time typing all the explanations. Stay safe and gave a nice day!